A typical automobile engine starter includes a solenoid that is activated upon closing an ignition switch. As shown in FIG. 7, the typical solenoid includes two terminals 110 and 112 positioned within a solenoid cap 116 on the end of the solenoid. The cap 116 is generally comprised of a non-conductive material, such as a plastic, that insulates the terminals from each other. A contact 114 for establishing an electrical connection between the terminals 110 and 112 is also provided within the cap 116. The contact 114 is provided as a metal plate secured to the end of a rod 118. The contact plate 114 and rod are biased by a return spring 120 away from the terminals 110 and 112. The opposite end of the rod 18 from the contact plate 114 is coupled to a solenoid plunger. When the operator of the automobile cranks the engine by turning a key, an ignition switch is closed and electric current is provided to the solenoid windings. Upon excitation of the solenoid, the plunger shifts in position and forces the rod 118 and the contact 114 toward the terminals 110 and 112 until the contact plate 114 comes into contact with the terminals 110 and 112. When the contact 114 physically touches the terminals 110 and 112, an electric circuit is completed which provides cranking current to the starter motor.
FIG. 8 shows an exemplary contact 114 for a starter motor. The exemplary contact 114 is provided as a flat and rectangular plate with two side portions 120 and 122 separated by an enlarged center portion 124. The contact plate 114 includes a first terminal face 121 and a second terminal face 123. A hole 126 is provided in the center portion 124 which allows the plate 114 to be connected to a contact rod 118. The edges 128 of the contact plate 114 are well defined, resulting in sharp edges along the contact 116. The edges 128 of the contact plate meet at corners 129 that are also well defined and sharp.
FIG. 9 shows the contact plate of FIG. 8 positioned in a solenoid cap 116. The solenoid cap of FIG. 9 is shown at a 90° angle compared to the cap shown in FIG. 7 such that only one of the terminals 112 is seen in FIG. 9. The contact plate 114 slides back and forth within a channel 130 formed in the solenoid cap 116. The contact plate 114 is arranged in the channel 130 of the solenoid cap 116 such that the sides of the contact plate 114 are closely positioned along the channel walls 131.
In a high vibration environment, as may be seen with certain vehicles at starting, the edges 128 and corners 129 of the contact plate 114 will bump into the channel walls 131. Back and forth movement of the contact plate 114 along the channel in such a high vibration environment causes the sharp edges 128 and corners 129 of the contact plate 114 to wear against the channel walls 131, digging into the channel walls 131 and creating a groove in the cap 116. This wear on the channel walls also results in the creation of a non-conductive dust that may settle on the terminal 112. The non-conductive dust may eventually result in a non-conductive covering on the terminal 112 that prevents the contact 114 from establishing an electrical connection between the two terminals. When this happens, a click-no-crank situation results, where the solenoid is activated, but power is not delivered to the starter motor because the contact never establishes an electrical connection between the terminals. Accordingly, it would be advantageous to provide a starter solenoid capable of operating in a high vibration environment without the contact plate wearing on the sides of the solenoid cap.